Sporting games involving rules around boundaries depend on the decisions of human judges or players themselves (for amateurs). For example, in tennis one needs to trace a position of a relatively small (approximately 6.5 cm in diameter) tennis ball, often traveling at relatively high speed (up to 65 msec) over a relatively large area of tennis court (24 m long by 11 m wide). Human errors of judging positions of tennis ball relative to boundary lines of court are inevitable.
Due to details previously mentioned, it is crucial to build a commercially viable system for automatic judging of boundary lines for tennis courts.
There have been known attempts to develop and patent such a system.
For example, U.S. Pat. No. 5,303,915 of Candy et al. describes a system, in which positions of bouncing of tennis ball are defined by interaction of special conductive tennis ball with electrical coils, buried beneath surface of a court.
Other system according to the U.S. Pat. No. 5,082,263 of Berger includes location of special tennis ball, equipped reflective elements, by radar.
Both above mentioned systems are not acceptable, because they demand change of standard equipment of the game (tennis ball or surface of court).
There are also systems, not demanding change in standard equipment of game and using video cameras for remote location of a tennis ball.
One such a system (U.S. Pat. No. 5,489,886 of Wexler et al.) uses up to 30 video cameras, situated along boundary lines of court and other places. Its major complexities have deemed this system unviable.
Other such system (U.S. Pat. No. 6,233,007 of Carlbom et al.) suggests using pairs of video cameras for stereo 3-Dimensional location of tennis ball. This system demands quite complex processing of stereo images and needs, evidently, an abundance of video camera's pairs for reliable working (which in turn make it complex and expensive).
Another such a system (described by M. Fischetty in article “In or Out?” in Scientific American, July 2007, pp. 96-97) named “Hawkeye” and widely used in major tennis tournaments (and broadcastings) is comprised of 10 video cameras and 14 computers for 3-Dimensional location of tennis ball. The system is very complex, requires large processing power and complicated software, and of course is very expensive (setup and operation cost is up to $50000 a week per court). This system of course is not affordable for numerous non professional tennis clubs.
Other such system and method for judging boundary lines in court by video cameras exists (U.S. Pat. No. 6,816,185 of Harmath). This system continuously defines the trajectory of a tennis ball and detects a spot on the court where the ball bounces by locating within its trajectory a sudden change in direction and calculating coordinates of this change relative to boundaries of the court.
But such a system has essential drawbacks. First of all the notion itself of “a sudden change in direction within the trajectory” is defined unclearly and inexactly to be implemented reliably and with high precision. Then, because of geometry of watching, sudden change of trajectory of the tennis ball, caused by bouncing from court and seen by one or a few video cameras, may be so insignificant in some part of the court, that registration of this change will have low precision and reliability and will be often impossible (in connection with geometry of watching every video camera can have “blind” areas for registration of these changes). Building a system according to this patent may demand the use of extremely high speed and resolution video cameras (what was pointed out in the patent itself) and using possibly many video cameras. This may lead to higher processing power of computing system and make the described system in whole quite complex and expensive.
So there is a need for a relatively simple and inexpensive system for automatic judging of the tennis ball's bouncing position relative to boundary lines of court, where such a system would be affordable especially for numerous non professional tennis clubs.
This purpose is served by the present invention.